1. Technical Field
The present invention relates generally to semiconductor wafers and more particularly the invention pertains to the field of Chemical Mechanical Polish (CMP) used during the fabrication of semiconductor chips to planarize the wafers.
2. Background Art
Rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections which connect active areas. As a result, the tolerances regarding the planeness or flatness of the semiconductor wafers used in these processes are becoming smaller and smaller. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus.
Such a polishing apparatus has a rotating wafer carrier assembly in contact with a polishing pad. The polishing pad is mounted on a rotating turntable which is driven by an external driving force. The polishing apparatus causes a polishing or rubbing movement between the surface of each thin semiconductor wafer and the polishing pad while dispersing a polishing slurry to obtain a chemical mechanical polish (CMP). CMP in planarization requires the wafer surface to be brought into contact with a rotating pad saturated with either a slurry of abrasive particles or a reactive solution, or both, that attacks the wafer surface. This is done while exerting force between the wafer and polishing pad. The abrasive particles can scratch the surface during the polish operation especially if they agglomerate. Also, after polishing is completed and the wafer is rinsed to remove the abrasive particles, some of the abrasive particles will remain on the wafer surface by simply being imbedded into the surface or strongly attracted to the surface.
The scratches can cause problems in subsequent processing steps as for example in a Damascene process, intra-level where shorting could result. Leaving the particles on the wafer can likewise lead to process problems, most notably photolithographic and etching defects in subsequently processed levels.
Prior art for particle removal involves either a mechanical clean, such as a brush clean, after the wafers have been removed from the polishing apparatus and dried, or a washing step with a surfactant (soap) performed prior to the wafer being dried as disclosed in U.S. Pat. No. 5,320,706, issued to Blackwell on Jun. 14, 1994 and assigned to Texas Instruments Incorporated. These processes are not usually 100% effective and do not address the scratching problem. Therefore, it appears that no prior art per se exists that addresses the scratching problem directly.